Composite materials in brought terms are known from the state of the art, such as for example from international application WO-01/02165. In such a composite material the core material (which determines by far the largest component of the composite material) mainly determines the bulk mechanical properties of the composite material, such as for example the strength thereof. The clad sheet however (which, consequently, only determines a small fraction of the composite material and thus will be of minor importance for the mechanical properties thereof is in contact with the environment surrounding the composite material and thus will determine the chemical activity, for example to a very large extent the corrosion performance of the composite material.
As examples of aluminium composite materials according to the state of the art firstly brazing sheet having typically an aluminium alloy from the AA3xxx-series as core material (e.g. AA3003) and on one or both sides thereof an aluminium alloy from the AA4xxx-series (e.g. AA4045 or AA4343) as clad sheet, as well as sheets for aeronautical use (core material comprising an aluminium alloy from the AA2xxx-series and clad sheet typically comprising an aluminium alloy from the AA1000-series) such as Alclad 2024-1230 may be mentioned. It is common for such known composite materials that these are developed for a specific use and for fulfilling specific demands.
U.S. Pat. No. 6,329,075-B1 discloses an aluminium alloy composite sheet having a core material of high strength and one or more claddings layers having an electrical conductivity greater then the core material for improved performance in heat exchanger applications. The core material is made from an alloy selected from the group of an AA3000, an AA6000, and an AA8000-series aluminium alloy, and the core alloy having an electrical conductivity less than 50% IACS, and the cladding is selected from the group of an AA1000 and AA7000-series aluminium alloy while having an electrical conductivity of greater than 50% IACS. The composite material is for brazing applications and can be made in any form, corrugated fin stock, tubing, headers, or any other shape that would be adapted for brazing.
International application WO-98/24571 discloses a multilayer metal composite product obtained by compound strand casting. The product comprises a core, preferably an aluminium alloy, on at least one side of the core an interlayer bonded to the core and a cladding bonded to the interlayer. Depending on the application of the product, the cladding forming the outersurface of the composite product can be a aluminium brazing alloy for use in brazing sheet, an AA1xxx-series alloy to obtain a mirror like surface finish, or an zinc containing aluminium alloy or zinc or a zinc alloy to improve corrosion resistance.
As will be appreciated herein below, except as otherwise indicated, all aluminium alloy designations refer to the Aluminum Association designations in Aluminium Standards and Data and the Registration Records, as published by the Aluminium Association in 2006.
For this invention “sheet product” refers to a rolled product form over 0.15 mm through 2.5 mm in thickness with sheared, slit, or sawed edges.
For this invention “automotive body sheet” or “ABS” refers to aluminium alloy sheet for automotive body applications, in particular exterior panels, interior panels and structural parts.
For any description of alloy compositions or preferred alloy compositions, all references to percentages are by weight percent unless otherwise indicated.